Studio Build: Garage Conversion in Los Angeles

[Jag94]

Hey Starlight, thanks for the quick reply (as always).

A silencer is basically an empty box. If you put that in a wall then the wall will not have mass at that place and it will be an isolation weak spot, a place where sound leaks in or out - as a drummer, perhaps more the latter. In principle it does not sound like the right plan.

I think I didn't articulate what I meant very well. I'll rephrase it, and see if you still have the same answer so we can be sure we're on the same page. So that north wall where the garage door is (and where I have the ERV in the sketchup picture), actually has a large gap between the interior wall and the exterior wall (garage door with new wall in place). My alternate plan was to place the silencers in that space between the inner and outer leafs. I looked at your build thread that you linked to, and I would equate it to how you have your silencer boxes mounted on the wall outside of your studio. Does that make any sense?

The 8" ducts went up in my room only last week, here. I am guessing you will use 4" or 6". Mine looks sort of industrial at the moment with the duct wrap. Is that the look you are wanting?

Yeah I guess that's what I was envisioning. I will have ceiling clouds with recessed lights hanging from the ceiling, so maybe the ducts won't be as noticeable because the clouds will be taking up much of the ceiling.

The ceiling on the east/west walls will be angled, much like your acoustic treatment on the left and right of the photo. So it's not exactly a corner like it would be in a standard rectangular room. I don't know what I'm going to do about treatment yet though.

Is round duct better than square duct? Also, Should I be using solid duct or flex duct? Does it matter?

Source of the post Greetings jag94,

From your illustration of the silencers, one thought has occurred to me: in the "vertical" orientation you're showing, you might want to add another stud (and possibly beef them up) to support the boxes. Gravity will be working against you, and the weight distribution is something to consider.

Paul, that's a great point. Those silencer boxes might end up quite huge. The sketchup was just an idea and not to scale, so I don't know how big they'll be yet, but in any case, having some extra support for hanging them is a great idea.

[SoWhat]

Greetings jag94,

Those silencer boxes might end up quite huge.

Count on it.

All the best,

Paul

[Starlight]

Source of the postMy alternate plan was to place the silencers in that space between the inner and outer leafs. Does that make any sense?

I can see why you would want to place a silencer there. Would that limit (and in some way compromise) the sealed air space in the two mass layers, the inner and outer walls? It depends, to some extent, on how critical isolation is. With you being a drummer I would guess fairly critical.

One further thought. In theory you should never need to access your silencers but as one will be constantly carrying outside air indoors, maybe over time some bugs, condensation, rotted duct liner (more so if you use a foam liner than a mineral wool or glass fibre liner) may give you cause to access the silencers. As per your plan you would need to break down a wall. I am not saying you will, I am just thinking what would make life easier whould you ever need to. Maybe you won't. I don't have enough experience to guide you on this.

Source of the postIs round duct better than square duct?

The question is: which has the larger cross sectional area? The larger the duct the slower and quieter the air will travel.

Source of the postShould I be using solid duct or flex duct?

I know studio designers that suggest solid because the inside is smoother and therefore creates less turbulece, meaning the air travels quieter. I also know studio designers that always use flexible duct because it allows more sound to get trapped in the insulation which is between the inner and outer foil layers. I studied and made my choice; I think you will need to do the same unless Stuart has enough time to contribute here.

[Jag94]

I know studio designers that suggest solid because the inside is smoother and therefore creates less turbulece, meaning the air travels quieter. I also know studio designers that always use flexible duct because it allows more sound to get trapped in the insulation which is between the inner and outer foil layers. I studied and made my choice; I think you will need to do the same unless Stuart has enough time to contribute here.

Perhaps using solid for inside the room, and flex in between the walls will work well. Thanks for the tip. I think I have a good idea where to start.

[Starlight]

Most definitely use flexible duct between the walls because solid duct would join the walls and create a flanking path.

[Jag94]

Source of the post Most definitely use flexible duct between the walls because solid duct would join the walls and create a flanking path.

Wait, flexible duct won't create a flanking path? I had seem some other threads where people built some sort of de-coupler that separates the duct at some point so as to decouple the duct so it doesn't transfer sound between leafs. It would be awesome if all I needed was flex duct and not have to worry about a decoupler.

I am trying to learn how this HVAC system will work, and making sure I calculate everything properly so I don't create any major issues with the design. This HVAC stuff is completely foreign to me, so bare with me.

The duct size on the ERV unit I'm going to use is 5". Since the unit is in the room and the fresh air duct and the stale air return will also be in the room and not going through the inner leaf, is it best to just use 5" ducts all the way around the interior?

When I calculated the cross sectional diameter from the specs of my mini-split unit and the specs from the ERV, it looks like I should be using 8" ducts. So Will I use 8" ducts to bring the air in from outside and into the silencer box, then the other end of the silencer box goes into the ERV with a 5" duct and then into the room with a 5" duct? and the same with the return. The air from the room goes into the ERV via the 5" duct, the another 5" duct to the silencer box. From the silencer box (through the wall) to the outside will be an 8" duct?

When I'm calculating the static pressure, is it the total duct length (plus elbows, registers, take-offs, flanges, etc.) of each port of the ERV combined? Or do you calculate each port separately? For example, the ERV has 4 ports (fresh air from outside, fresh air to inside, stale air from inside, and stale air to outside). Am I finding the static pressure separately for each port (and making sure each port is within the specs of the unit), or am I taking the result of each port and adding it all together, and making sure THAT number is within the specs of the unit? Or is it something else? Since there are 2 fans (one bringing in fresh air, and one taking out stale air), am I calculating the static pressure for each fan?

I found a formula for building the proper size of the silencer boxes, but it all depends on the side ducts that I'm using. At this point I've read so many damn build threads that they're starting to mush all together, and it's hard for me to find the ones that had a lot of the better info.

[Starlight]

Source of the postWait, flexible duct won't create a flanking path?

This post by Rod Gervais tells us in the 3rd paragraph that he uses flexible duct to isolate. Alternatively, I came across this (see the 9th photo) which you might prefer. At the time I didn't understand what he had done but I do now: the two outer metal rings are duct connectors, things you use to connect two lengths of straight duct together, to which he has simply attached a length of material. Here is my studio with the flexiduct bridging the two walls, following Rod Gervais's comment.

Source of the postThe duct size on the ERV unit I'm going to use is 5". ... So Will I use 8" ducts to bring the air in from outside and into the silencer box, then the other end of the silencer box goes into the ERV with a 5" duct and then into the room with a 5" duct? and the same with the return. The air from the room goes into the ERV via the 5" duct, the another 5" duct to the silencer box. From the silencer box (through the wall) to the outside will be an 8" duct?

5" duct has a cross section of 20". 8" duct has a cross section of 50". That means the same amount of air will travel signficantly slower in 8" duct than in 5". Slower = quieter. The ideal situation would be 8" everywhere and use 5" to 8" adapters on all four ports on the ventilator, like this:

Source of the postWhen I'm calculating the static pressure ...

I struggled with this. Jennifer has a better understanding of the calculations or you can ask Stuart to check them (and pay him by way of a suitable donation).

[Jag94]

This post by Rod Gervais tells us in the 3rd paragraph that he uses flexible duct to isolate. Alternatively, I came across this (see the 9th photo) which you might prefer. At the time I didn't understand what he had done but I do now: the two outer metal rings are duct connectors, things you use to connect two lengths of straight duct together, to which he has simply attached a length of material. Here is my studio with the flexiduct bridging the two walls, following Rod Gervais's comment.

Ok great. I'll read up on those tonight. I did read through your thread and saw how you used the flex ducts in between walls. Thanks for the info.

5" duct has a cross section of 20". 8" duct has a cross section of 50". That means the same amount of air will travel signficantly slower in 8" duct than in 5". Slower = quieter. The ideal situation would be 8" everywhere and use 5" to 8" adapters on all four ports on the ventilator, like this:
Duct.jpg

Ok this makes a lot of sense. I think I had it backwards (which would have created faster/noisier airflow). Having the 5" port go to 8" ducts for the fresh/stale air in the room makes sense. When I'm going from the ports to the silencer boxes, I would still want 5" to 8" adapters with 8" ducts going to the silencer, air travels through silencer, and then also 8" ducts from the silencer through the inner wall and to the outside?

Is it OK to use a solid 90° elbow with flex duct to make sure the duct doesn't get choked or restricted in any way?

I struggled with this. Jennifer has a better understanding of the calculations or you can ask Stuart to check them (and pay him by way of a suitable donation).

I actually just read that as long as the duct length is under 100 ft, you don't even have to worry about calculating. And mine won't even come close to that.

Also, I did make a donation to the site, although not as much as I wanted to because I am officially over budget for this project, and still unemployed from COVID. haha.

[Jag94]

Source of the post

This post by Rod Gervais tells us in the 3rd paragraph that he uses flexible duct to isolate. Alternatively, I came across this (see the 9th photo) which you might prefer. At the time I didn't understand what he had done but I do now: the two outer metal rings are duct connectors, things you use to connect two lengths of straight duct together, to which he has simply attached a length of material. Here is my studio with the flexiduct bridging the two walls, following Rod Gervais's comment.

Ok great. I'll read up on those tonight. I did read through your thread and saw how you used the flex ducts in between walls. Thanks for the info.

5" duct has a cross section of 20". 8" duct has a cross section of 50". That means the same amount of air will travel signficantly slower in 8" duct than in 5". Slower = quieter. The ideal situation would be 8" everywhere and use 5" to 8" adapters on all four ports on the ventilator, like this:
Duct.jpg

Ok this makes a lot of sense. I think I had it backwards (which would have created faster/noisier airflow). Having the 5" port go to 8" ducts for the fresh/stale air in the room makes sense. When I'm going from the ports to the silencer boxes, I would still want 5" to 8" adapters with 8" ducts going to the silencer, air travels through silencer, and then also 8" ducts from the silencer through the inner wall and to the outside?

Is it OK to use a solid 90° elbow with flex duct to make sure the duct doesn't get choked or restricted in any way?

I struggled with this. Jennifer has a better understanding of the calculations or you can ask Stuart to check them (and pay him by way of a suitable donation).

I actually just read that as long as the duct length is under 100 ft, you don't even have to worry about calculating. With the 90° turns I have in my design, that puts me at 100ft right there, plus the actual length of the ducts (which I figure to be about 50-60ft). So maybe it's the total amount of ducts. I'll reach out to the manufacturer as well to see what they say.

Also, I did make a donation to the site, although not as much as I wanted to because I am officially over budget for this project, and still unemployed from COVID. haha.

[SoWhat]

Greetings jag94,

When I'm going from the ports to the silencer boxes, I would still want 5" to 8" adapters with 8" ducts going to the silencer, air travels through silencer, and then also 8" ducts from the silencer through the inner wall and to the outside?

It's a good idea.

When you build your boxes, use a router to cut the circular openings. Much easier than a saw, and you can even get a jig (or make your own), for the circles.

All the best,

Paul

[Starlight]

Source of the postWhen you build your boxes, use a router to cut the circular openings.

If you don't have a router make a jig for your jig saw - see the last photo in post 92, here.

I cut my silencer holes with a jig saw but without a jig, freehand circles. Sealing the duct in place with caulk means a not quite accurate 8" circle shouldn't be a problem. A router or jig saw with a jig would be neater.

[SoWhat]

I cut my silencer holes with a jig saw but without a jig, freehand circles.

Hands as steady as a surgeon.

I am truly impressed. I still probably can't color within the lines...

[Jag94]

It's a good idea.

When you build your boxes, use a router to cut the circular openings. Much easier than a saw, and you can even get a jig (or make your own), for the circles.

All the best,

Paul

Perfect. Now that I know how big to make my ducts, I can move on to the next step.

Thanks for the tip about the router. I do have one, and use it whenever I get the chance!

[Jag94]

Update and some questions.

I finally, FINALLY got started on building the interior leaf frame today. I thought this day was going to come a lot sooner, but beefing up the outer leaf took WAY longer than I had imagined. It's starting to feel like I am making progress. One thing that is tough, is since the room is so small, I'm constantly having to move things to make space to work. I spend so much time relocating materials and tools that I lose a half day of productivity. Now that the walls are being built, a substantial amount of space will start to open up in the room. By the time I'm ready for drywall, It's going to be really easy to move around in there.

I think I'm starting to get a good idea of this HVAC nonsense. Here is what I have so far, with update and more accurate numbers. Please tell me if I'm either missing something, or am wrong about something.

Interior room dimensions:
14'10" x 14'1" x 8'8"
= 1,810 cubic feet

With 6 room changes per hour = 10,860 cubic feet/hour

10,860 / 60 = 181 CFM for heating and cooling.

My mini split is very capable of handling this CFM.

181 x 40% = 72.4 CFM for the ERV

The ERV I'm now using can also handle this, even with a static pressure of 0.4 (I think maximum I'm looking at 0.2 for static pressure).

OK. So in determining duct size and silencer box size, here is what I have. This is the formula for the silencer box I will be using.

If I use an 8" round duct (to both bring the air in from outside, exhaust to outside, as well as bringing air to room from ERV, and from the room via ERV)...

8" round duct = Cross Sectional Area of 50.27 square inches. For a silencer box, I want to at least double the CSA inside the box (quadruple it would be better, but I can't afford that much space). So doubling the CSA gives me 100.53 square inches.

The square root of 100.53 = 10.26464. I'm going to upsize that to 10.5" (which is now 110.25 square inches).
10.5 is now my value for X in the silencer box above.

To calculate the velocity (feet per minute) of the air,

110.25 / 144 = .765625 square feet

(40% fresh air in CFM) / square feet
72.4 CFM / .765625 square feet = 94.563265 feet per minute.

This is good, because it's well under 300 fpm.

Using the formulas in the silencer box design above, I end up with a box dimension of...

53.5" x 28" x ??

I think I found the answer to the depth. I believe I saw a post on John Sayers sight saying the depth is a minimum of x + 4. Bigger is better, of course, but I think I am going to stick with that. Am I on the right track here?

[Starlight]

Gregwor's design shows that the width of the box is 2X+3 + 2 duct liners (2 * 1") + 2 wood thicknesses (2 * 1" MDF).

You decided that your X is 10.5".

So, 2 * 10.5" + 3 + 2 * 1" + 2 * 1" = 21 + 3 + 2 + 2 = 28". At least I agree with your 28" width.

Height, then, will be X + 2 duct liners (2 * 1") + 2 wood thicknesses (2 * 1" MDF) = 10.5" + 2 + 2 = 14.5".